Field addressable rewritable media

ABSTRACT

An electrochromic molecular colorant and a plurality of uses as an erasably writeable medium. Multitudinous types of substrates, such as paper, are adaptable for receiving a coating of the colorant. Electrical fringe field or through fields are used to transform targeted pixel molecules between a first, high color state and transparent state, providing information content having resolution and viewability at least equal to hard copy document print. The scope of the invention includes both the liquid coating and the combination of coating on substrate.

(2) CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] Not Applicable.

(3) STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0002] Not Applicable.

(4) REFERENCE TO AN APPENDIX

[0003] The present application includes a hard copy appendix comprisingpertinent specification pages and drawings of co-inventors' U.S. patentapplication Ser. No. 09/844,862, filed Apr. 27, 2001, by ZHANG et al.for MOLECULAR MECHANICAL DEVICES WITH A BAND GAP CHANGE ACTIVATED BY ANELECTRIC FIELD FOR OPTICAL SWITCHING APPLICATIONS (Hewlett-PackardCompany docket no. 10013977) as relates to subject matter claimed inaccordance with the present invention.

(5) BACKGROUND OF THE INVENTION

[0004] (5.1) Field of the Invention

[0005] The present invention relates generally to methods and apparatusfor distribution of information, more specifically to electronicallydisplaying informational content and, more particularly to a reusable,high contrast, very high resolution, rewritable print medium and methodsfor fabrication thereof.

[0006] (5.2) Description of the Related Art

[0007] Hard copy and, more recently, electronic display information iscommunicated in many forms and by many means. Erasable-rewritable printmedia communication tools range from simple pencil-on-paper tochalk-on-blackboard to dry marker pen-on-whiteboard. More sophisticatedhard copy processes allow mechanized business and commercial printingprocesses—including laser and ink-jet printers, offset lithography,silkscreen, and the like, for printing—but those processes are usuallyrestricted to the permanent print category (versus “erasable print” or“erasably writable” formats and methods). The bulk of print iscommercially produced and made available through books, magazines,newspapers, and various other forms of permanent ink (“toner” or, moregenerically “colorant”) on cellulose fiber media (commonly known as“paper”). The information content—generally alphanumeric text andgraphical images—contained in this form is of a sufficiently highresolution and contrast to be easily read over prolonged periods of timewithout eye discomfort. Compared to electronic devices, hard copy mediahas the advantages of having zero power consumption while remaininghighly portable, allowing comfortable reading in locations of choice andbody positions that may be periodically varied to change readingdistance and posture to maintain comfort. Such print media, however,requires a relatively high cost in printing, binding, warehousing, anddistribution. The hard copy cost, independent of printing means, isnormally amortized through a single reading, after which the book orother document is physically stored or discarded. Since these lattercost factors also require a definable time expenditure between contentgeneration and availability to the reader, the content of the media isnot contemporaneous; e.g., today's newspaper actually is filled with“what happened yesterday.”

[0008] Much print is created by hand, e.g., using pen or pencil onpaper. In many cases, such print is used for temporary informationstorage such as phone numbers, reminders, grocery lists, andappointments. Print media for such print commonly consists of notepads,Post-It® notes, calendars, tear-sheet display boards, and the like. Ineach instance, the medium is usually used for its intended purpose thenlater discarded or ignored, leading to waste, recycling costs, andclutter.

[0009] Chalk-on-chalkboard and dry marker pen-on-whiteboard printovercome issues of media waste and clutter. Such print images areproduced with powders or inks that coat the media surface withoutpermanent attachment, allowing easy image viewing, erasing, andsubsequent re-imaging. However, such print is not applicable to portablemedia applications, such as grocery lists, bound image applications, orother uses in which the media surface may be smeared by contact. Afurther disadvantage is the messy residue that results from the removalof the chalk or ink from the media surface.

[0010] Business printers, such as the ubiquitous laser and ink-jetprinters, in connection with the Internet overcome some of theseproblems and provide contemporaneous information distribution with anattendant hard copy printing availability, but at a higher cost per pageand usually at a lower quality or in a different format than commercialprint. (The term Internet is used herein as a generic term for acollection of distributed, interconnected networks (ARPANET, DARPANET,World Wide Web, or the like) that are linked together by a set ofindustry standard protocols (e.g., TCP/IP, HTTP, UDP, and the like) toform a generally global, distributed network. (Private and proprietaryintranets are also known and are amenable to conforming uses of thepresent invention.)

[0011] Computers, on the other hand, provide virtually instantaneousdistribution of content through the Internet at significantly reducedcost to the reader. Similarly, with the advent of handheld devices suchas palmtop computers, electronic books, net-ready telephones, and“personal digital assistants” (PDAs), print can be generated onelectronic displays of varying sizes and types. Computer displays,however, provide far less comfortable readability by displaying contentat significantly lower resolution than hard copy media. Cathode ray tube(“CRT”) displays have greater resolution capability but have lowportability, if any, and require substantially stationary bodypositioning and reading at a somewhat fixed focal length, leading tocomparatively rapid eye strain and posture discomfort. Liquid crystaldisplays (“LCD”) generally used in portable computers allow somewhatgreater portability, but at the expense of display contrast, off-axisviewability, and higher cost. In part, the lower resolution of portabledisplays stems from the difficulty of matrix addressing at higherresolution.

[0012]FIG. 1AA (Prior Art) exemplifies the basic operation of a flatpanel electronic display, such as a commercially available, flat panel,LCD 1 (dashed lines are used in this drawing to indicate continuation ofdiscrete elements of the apparatus so as to make the drawing lesscomplicated). Basically, the LCD 1 includes a plurality of pictureelements (“pixels”) defining the resolution of the display, generallyformed by an array of thin film transistors (“TFT”) and too small to beseen in this FIGURE (e.g., 600 dots per inch (“dpi”). A plurality ofgate lines 2 and data lines 3 form a pixel control grid for active area“B” of the panel 1. The gate lines 2 and data lines 3 extend as leads 5outside of the active area B for connection to known manner integratedcircuit drivers. A plurality of pads, one for each line, are formed inregion “C” about the periphery of the active area B as discrete padregions 4 are coupled by the leads 5 to the gate and data lines 2, 3.Color LCD is produced by backlighting the individually switched pixelscrystals through color filters. Note importantly that the resolution ofthe screen is limited by the technology related to interconnectwiring—namely, between the gate and data lines and the microprocessor ormemory sending data—and driver size for each pixel. Moreover, such adevice requires power to maintain each pixel in its current state andcontinually to backlight the crystal screen.

[0013] The at least one order of magnitude lower resolution of computerdisplays in comparison to commercial hard copy commonly prevents thereader from seeing a full-page comparable document at one time.Moreover, because of screen size constraints, without a very large videomonitor or shrinking the page to fit a screen, the reader must usemanual controls to scroll the displayed image down the document page inorder to read its entire content. Furthermore, graphic images often cannot fit on a single screen without severe zoom-out reduction in size,limiting the detail which can be displayed. Still further, there is therequirement of booting-up the computing device, turning on the specificapplication (notepad, calendar, or the like), and making at least oneuser command entry to obtain a document page of interest. More oftenthan not, rather than using a PDA to make a note, a simple notescribbled on a piece of paper is much more convenient.

[0014] In addition to the aforementioned shortcomings of electronicdisplays, such displays are relatively high in power consumption,particularly if the screen is of the active transistor type. Also, theysuffer from relatively poor contrast (viewability) in outdoor or otherbright ambient environment conditions. Emissive displays, such as CRT,plasma, light emitting diode (“LED”), and backlit LCD, haveself-illuminated picture elements (“pixels”). Emissive displays haveexcessive power consumption by virtue of the need to produce light. Suchself-illumination is still comparatively low in brightness and thereforeappears dark in bright ambient viewing conditions due to the eye'sautomatic adaptation to the ambient brightness. Non-backlit LCDs havepoor contrast under virtually all ambient illumination; the ambientlight reflected from each LCD pixel must pass through polarizers thatsignificantly reduce pixel brightness relative to ambient brightness.This makes the LCD appear dark and of poor contrast. Prior artelectronic displays used in computers and televisions have thereforebeen limited to practical use under controlled office and home ambientillumination. With the advent of mobile computer appliances, such asweb-based telephones, palmtop computers, and televisions, there is agrowing need for display technologies that provide good viewabilityunder the wider range of ambient illumination conditions in which userscommonly communicate, do business and are entertained. Mobile appliancesdemand low power consumption for long battery life. Therefore, there isa growing need for an alternative to conventional electronic displaysthat consume less power.

[0015] When a long document is downloaded from the Internet, the readerwill commonly print the contents to gain back the aforementioned hardcopy media benefits. Such printing, however, adds local cost to theprocess for documents that commonly are still read just once andeventually discarded. The recycling of paper barely makes a dent in themultiple costs to the environment. For information distribution, currentcomputer solutions are, thereby, still somewhat antithetical to theneeds for distribution of books, periodicals such as magazines andnewspapers, and the like.

[0016] Electrostatically polarized, bichromal particles for displayshave been known since the early 1960's. The need for an electronicpaper-like print means has recently prompted development of at least twoelectrochromic picture element (pixel) colorants: (1) amicroencapsulated electrophoretic colorant (see e.g., U.S. Pat. No.6,124,851 (Jacobson) for an ELECTRONIC BOOK WITH MULTIPLE PAGE DISPLAYS,E Ink Corp., assignee), and (2) a field rotatable bichromal colorantsphere (e.g., the Xerox® Gyricon™). Each of these electrochromiccolorants is approximately hemispherically bichromal, where onehemisphere of each microcapsule is made the display background color(e.g., white) while the second hemisphere is made the print or imagecolor (e.g., black or dark blue). The colorants are field translated orrotated so the desired hemisphere color faces the observer at eachpixel. FIGS. 1BB and 1CC schematically depict this type of prior art.

[0017] Electronic ink is a recent development. E Ink Corporation(Cambridge, Mass.; www.eink.com) provides an electronic ink in a liquidform that can be coated onto a surface. Within the coating are tinymicrocapsules (e.g., about 30 μm to 100 μm in diameter, viz. about asthick as a human hair, thus quite visible to the naked eye). Asillustrated in FIG. 1BB (Prior Art), each microcapsule 6 has whiteparticles 7 suspended in a dark dye 8. When an electric field is appliedand sustained in a first polarity, the white particles move to one endof the microcapsule where they become visible; this makes the surfaceappear white at that spot. A carrier 9 is provided. An opposite polarityelectric field pulls the particles to the other end of the microcapsuleswhere they are substantially hidden by the dye; this makes the surfaceappear dark at that spot.

[0018] The Xerox Gyricon sphere is described in certain patents. FIG.1CC (Prior Art) is a schematic illustration of this type of sphere. U.S.Pat. No. 4,126,854 (Sheridon '854) describes a bichromal sphere havingcolored hemispheres of differing Zeta potential that allow the spheresto rotate in a dielectric fluid under influence of an addressableelectrical field. U.S. Pat. No. 4,143,103 (Sheridon '103) describes adisplay system using bichromal spheres in a transparent polymericmaterial. U.S. Pat. No. 5,604,027 (Sheridon '027), issued Feb. 18, 1997,for SOME USES OF MICROENCAPSULATION FOR ELECTRIC PAPER, describes aprinter. Essentially, each sphere 10 (again, about 30 μm in diameter)has a bichromal ball 13 having two hemispheres 11, 12, typically oneblack and one white, each having different electrical properties. Eachball is enclosed within a spherical shell 14 and a space 15 between theball and shell is filled with a liquid to form a microsphere so that theball is free to rotate in response to an electrical field. Themicrospheres can be mixed into a substrate which can be formed intosheets or can be applied to a surface. The result is a film which canform an image from an applied and sustained electrical field. Currently,picture element (“pixel”) resolution using this Gyricon spheres islimited to about 100 dpi.

[0019] Thus, in the known prior art, each individual colorant device isroughly hemispherically bichromal; one hemisphere is made the displaybackground color (e.g. white) while the second hemisphere is made theprint or image color (e.g. black or dark blue). In accordance with thetext and image data, these microsphere-based colorant devices are fieldtranslated or rotated so the desired hemisphere color faces the observerat each respective pixel. It can be noted that, in commercial practice,displays made from these colorants have relatively poor contrast andcolor. The layer containing the microcapsules is generally at least 3 or4 microcapsules thick. Light that penetrates beyond the layer surfaceinternally reflects off the backside hemispheres causing color (e.g.black and white) intermixing. The image is, for example, thus rendereddark gray against a light gray background. Thus, these technologies donot provide a promising extendability and scaling to high resolutioncolor displays because the colorant switches only between two opaquecolors, disallowing passage of light from different colorant layers fora given pixel. Still further, as is these colorant technologies producea visually poor display resolution relative to hard copy print due tothe relatively large size of the colorant microcapsule spheres.Moreover, the spheres are bichromal, limiting application to two-colorrather than true full color display. Further still, the need foroverlapping spheres in multiple layers to achieve adequate color densitylimits pixel resolution Yet another limitation is that these coloranttechnologies suffer from poor pixel switching times in comparison tostandard CRT and LCD technology. Each technology relies on theelectrophoretic movement of colorant mass in a dielectric material, suchas isoparafin. The color rotation speed of dichroic spheres underpractical electrical field intensities is in the range of 20milliseconds (ms) or more. At that rate, a 300 dpi resolution printeremploying an electrode array would be limited to under one page perminute print speed. These large sphere colorants require high switchingvoltages (e.g. 80-200 volts) to obtain adequate fields through theconsequently thick (>100 μm) carrier-colorant layer. Such switchingvoltages add high cost to the pixel drive electronics, similar to thatof the high-end matrix LCD apparatus. Thus, those involved in thedevelopment of microcapsule type colorants are struggling with theresolution of these and other related problems rather than focusing on anew molecular level technology as described in accordance with thepresent invention.

[0020] There are limitations to microcapsule technologies. The Gyriconmicrocapsule technology produces limited resolution compared to hardcopy due to the relatively large size of the microcapsule spheres,typically a diameter greater than 30 μm. As schematically illustrated inFIGURE 1DD (Prior Art), overlapping spheres in multiple layers areneeded to achieve adequate color density, limiting pixel resolution tothe order of 300-400 dots-per-inch (“dpi”), whereas, depending on theviewing conditions, the unaided human eye can discriminate to over 1000dpi. Displays made from microcapsules tend to have poor contrast andcolor because light that penetrates beyond the surface layer ofmicrocapsules reflects back off subjacent microcapsules causing colorintermixing. As also demonstrated in FIG. 1DD, poor image contrastarises from backside reflections from each microcapsule. Light enteringand penetrating the interstices of a first layer of microcapsules (nowillustrated as hemispherically colored black and white circles 8) in themedia surface coating 16 reflects and is absorbed by the backside, aswell as front side, hemispheres of subsequent microcapsule layers. Lowcolor density areas of the image become darker and high color densityareas become lighter than would otherwise occur if the microcapsuleswere of uniform color throughout their exterior (as is true withpigments, and dyes used in standard printing processes). Thus, in adevice using layers of bichromal microcapsules, the image is oftenactually rendered dark gray against a light gray background

[0021] Another limitation to achieving high contrast is that themicrocapsules of the type shown in FIG. 1BB superimposes the twoencapsulated components so that independently of which colorant facesthe observer, the second colorant is also visible. Because of the finitenature of the white particles 7 and dark color dye 8, when the whitehemisphere is displayed (rotated toward the viewer), dye will still showin the interstitial spaces between the white particles; likewise, whenthe dye hemisphere is displayed, the inherent transparent nature of thedye allows reflection toward the viewer off the subjacent whiteparticles, lightening the dye color (e.g., deep blue to a medium blue).In other words, neither one hundred percent reflection of white nor onehundred percent of absorption is achieved. Of the type of microcapsuleas illustrated in FIG. 1CC, while the hemispheres are opaque black andopaque white, respectively, when light hits the ball 13 it also goesbetween the spheres 10 similarly to as shown in FIG. 1DD, again limitingcontrast and resolution capability.

[0022] Furthermore, because they rely upon the electrophoretic movementof a mass in a liquid, these microcapsule technologies suffer from poorpixel switching times in comparison to standard CRT and LCD screens.Color switching comprises the relative rotational or translationalmovement of solid particles and liquid from the forward facing tobackside facing hemispheres. Relatively slow color switching time is thesimple result of the microcapsule's mass and fluidic drag within thesphere. The combined mass and fluidic drag define the time required toaffect a color switch at a given pixel. This, in turn, defines both theswitching energy requirements and the imaging speed, or “throughput,” ofa printer using media with this technology.

[0023] Further still, these relatively large microcapsules require highswitching voltages (e.g., 20-200 volts) to obtain adequate fieldsthrough the relatively thick (greater than 100 μm), multiplemicrocapsule layers 16. Such switching voltages add further cost to thepixel drive electronics, making it comparable to the cost of an LCDscreen.

[0024] Still further, these microcapsule technologies do not provide apromising extension to high resolution color displays because thecolorant switches only between two opaque colors, disallowing passage oflight from different colorant subjacent layers for a given pixel. Inother words, microcapsule colorant is not a true dye where outside theparticular dye absorption bandwidth the colorant becomes transparent,allowing different layered chemical compositions to render full colorimages (e.g., as used in color film and print technology). Thus, to gaina full color adaptation, microcapsule colorant based devices will belimited to mosaic patterning which further limits resolution and,ultimately, print quality.

[0025] Moreover, the microcapsules themselves suffer from difficultmanufacturing processes and relatively poor durability. Microcapsules,by their nature, have thin walls that are subject to breakage withsubsequent liquid leakage that destroys colorant functionality. Wallthickness is typically of the order of 1-2 μm (or about 10% ofdiameter). Microcapsule breakage may occur by pressure externallyapplied to the media surface, media folding, and by the coating processitself used to make the media. This limits the ability of the displaymedia to be folded or even contacted without a high probability ofcapsule breakage and subsequent loss of imaging function.

[0026] It can be concluded that there is not a currently availableelectronic information-displaying mechanism which does not have at leastsome of the foregoing described limitations. More particularly withrespect to the present invention , among the collection of present printand display state-of-the-art technologies there does not exist arewritable media capable of commercial hard copy resolution, contrast,and durability. Further, there is not a rewritable media that has thefull color quality appearance nor print readability of commerciallyprinted paper. Thus, there is a need for new and improved print media.

[0027] Still further, there is not an electronic rewritable media havinggood bright ambient illumination viewability and low power consumption.

[0028] Still further in the state-of-the-art, for digital data, massstorage media is another form of “rewritable media.” Conventional massstorage media includes disks and tapes having a magnetic surfacecoating. The surface coating used in disks and tapes generally containsa thin film deposition, or polymer suspension, ferromagnetic crystallayer. When exposed to an externally applied magnetic field, theferromagnetic crystals develop a residual magnetic field that remainsstable in the absence of the external field. The surface coating iswritten for data storage by a magnetic writing head translated (by diskrevolving or tape streaming) relative to the surface coating. Data isstored in the form of patterns of residual magnetic fields over thesurface. The data is retrieved by a magnetic read head (e.g., anelectric coil) translated relative to the encoded coating surface,transforming the residual magnetic field patterns into an oscillatingelectrical current stream representing the original electronic dataform. The area density and field strength of the magnetically recordeddata is determined by the size of the ferromagnetic crystal domains. Inan alternate form, digital data is stored on CD-ROM media in the form ofa pattern of laser-ablated or impressed pits on the surface of a lightreflective disk. The data is read optically as the disk rotates byreflecting light off the surface into a light sensor. The sensed signalchanges as it alternately strikes pits and reflective regions betweensuccessive pits. The density of data storage on the disk is a functionof the size of the ablated pits and intervening reflective regions. Ingeneral, data can be read from a CD-ROM at a significantly greater ratethan data can be written, since writing requires physical ablation ofmaterial in making pits. However, at present, writable CD technology isin its infancy and quality apparatus is relatively expensive.

[0029] With the ever-increasing need to store more data on storagemedia, there is increasing need for rewritable storage data storageelements that are much smaller than available through conventionalmagnetic and CD-ROM media, creating a higher data density capability.There is also a need to write data at higher data rates.

[0030] There is a need for a new technology for the field of displayinginformation that is adaptable to a wide range of implementations.Molecular science holds the promise for solution to many, if not all, ofthe shortcomings of the conventional methods and apparatus currentlyavailable for erasable writing and data storage, retrieval and display.Thus, the present invention provides molecular level solutions, viz.,molecular systems in the form of molecular level optical switches, thatcan be assembled easily to make displays, electronic books, rewritablemedia, electronic lenses, electrically-controlled tinting for windowsand mirrors, optical crossbar switches for fiber optic communications,and much more.

[0031] Due to the nature of the present invention which reaches intomolecular science technology, it will become apparent to the reader thatthere also arises a question as to what is “print media” and what is a“writing surface” and what is a “display screen” (more simply “display”or “screen” as best fits the context). In some implementations,discriminating as to which conventional definition such an apparatus ormethod of use falls into may be less than clear. Therefore, it should benoted that no limitation on the scope of the present invention isintended by the use of such a particular conventional term whendescribing the details and no such limitation should be impliedtherefrom. Thus, further limitations regarding convention displays isappropriate to understanding the need for and objects and advantages ofthe present invention.

(6) BRIEF SUMMARY OF THE INVENTION

[0032] In its basic aspect, the present invention provides a colorantfor a substrate, the colorant including: a molecular system, said systemincluding electrochromic, switchable molecules, each of said moleculesbeing selectively switchable between at least two opticallydistinguishable states, wherein said system is distributable on thesubstrate thereby forming an erasably writable surface. In anotheraspect, the present invention provides a writeable-erasable coating fora substrate, including: a carrier; and within said carrier, acomposition including electrochromic switchable molecules, each of saidmolecules being selectively switchable between at least two opticallydistinguishable states, wherein said molecules are distributable on thesubstrate thereby forming an erasably writable surface. Another aspectof the invention is an erasable writing medium including: a substrate;and at least one layer of a molecular colorant coating affixed to saidsubstrate, wherein molecules of the coating are at least bichromal andselectively switchable between color states under influence of alocalized electric field. Still another aspect of the invention is amethod for writing on electrical field addressable rewritable mediumincluding: providing a substrate having at least one layer of amolecular colorant coating wherein molecules of the coating are at leastbichromal and subjectable to switching between color states underinfluence of a localized electric field and wherein said layer isdistributed across said substrate forming pixels on said medium; andelectrically addressing pixels by selectively controlling each saidlocalized electric field to form document content on said medium.Another aspect of the present invention is a data storage deviceincluding: a substrate; and at least one layer of a molecular colorantcoating wherein molecules of the coating are at least bichromal andsubject to bistable switching between at least two electro-opticalstates under influence of a localized electric field. Still anotheraspect of the present invention is a method of fabricating rewritablemedia including: providing a substrate; and forming with said substrate,a rewritable layer wherein the writable-erasable layer is formed by amolecular system, said system including electrochromic switchablemolecules, each of said molecules being selectively switchable betweenat least two optically distinguishable states.

[0033] It is an important advantage and novel feature of the presentelectronic media that rendered images are of a quality as good as orbetter than conventional, very high resolution, ink-on-paper and can berendered as good as any photographic print.

[0034] The foregoing summary is not intended to be an inclusive list ofall the aspects, objects, advantages, and features of the presentinvention nor should any limitation on the scope of the invention beimplied therefrom. This Summary is provided in accordance with themandate of 37 C.F.R. 1.73 and M.P.E.P. 608.01(d) merely to apprise thepublic, and more especially those interested in the particular art towhich the invention relates, of the nature of the invention in order tobe of assistance in aiding ready understanding of the patent in futuresearches. Objects, features and advantages of the present invention willbecome apparent upon consideration of the following explanation and theaccompanying drawings, in which like reference designations representlike features throughout the drawings.

(7) BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In accordance with 37 C.F.R. 1.84(u), in order to preventconfusion with FIGURES of the Appendix hereto, the drawings of thisapplication use double capital letter suffices.

[0036]FIG. 1AA (Prior Art) is an elevation view schematic of an LCDscreen apparatus.

[0037]FIG. 1BB (Prior Art) is an exemplary electronic ink device.

[0038]FIG. 1CC (Prior Art) is a schematic depiction of a Xerox Gyriconsphere.

[0039]FIG. 1DD is a schematic drawing illustrating the physicsassociated with the prior art as illustrated in FIGS. 1BB and 1CC.

[0040]FIG. 2AA is a schematic depiction in a magnified, perspective viewof a unit of print media in accordance with the present invention.

[0041]FIG. 2BB is a magnified detail of FIG. 2AA.

[0042]FIG. 3AA is a schematic drawing of a first method and apparatusfor writing-erasing in accordance with the present invention as shown inFIGS. 2AA and 2BB.

[0043]FIG. 4AA is a schematic drawing of a second method and apparatusfor writing-erasing in accordance with the present invention as shown inFIGS. 2AA and 2BB.

[0044]FIG. 5AA is an alternative embodiment of the present invention asillustrated by FIGS. 2AA-4AA.

[0045]FIG. 6AA is an electrical schematic diagram in accordance with thepresent invention.

[0046]FIG. 7AA is a schematic drawing illustrating the physicsassociated with the present invention as shown in FIGS. 2AA-4AA forcomparison to FIG. 1DD.

[0047] The drawings referred to in this specification should beunderstood as not being drawn to scale except if specifically annotated.

(8) DETAILED DESCRIPTION OF THE INVENTION

[0048] Reference is made now in detail to a specific embodiment of thepresent invention, which illustrates the best mode presentlycontemplated by the inventors for practicing the invention. Alternativeembodiments are also briefly described as applicable. Subtitles are usedhereinafter merely for the convenience of the reader; no limitation onthe scope of the invention is intended thereby nor should any suchlimitation be implied therefrom.

[0049] Definitions

[0050] The following terms and ideas are applicable to both the presentdiscussion and the Appendix hereto.

[0051] The term “self-assembled” as used herein refers to a system thatnaturally adopts some geometric pattern because of the identity of thecomponents of the system; the system achieves at least a local minimumin its energy by adopting this configuration.

[0052] The term “singly configurable” means that a switch can change itsstate only once via an irreversible process such as an oxidation orreduction reaction; such a switch can be the basis of a programmableread-only memory (PROM), for example.

[0053] The term “reconfigurable” means that a switch can change itsstate multiple times via a reversible process such as an oxidation orreduction; in other words, the switch can be opened and closed multipletimes, such as the memory bits in a random access memory (RAM) or acolor pixel in a display.

[0054] The term “bistable” as applied to a molecule means a moleculehaving two relatively low energy states (local minima) separated by anenergy (or activation) barrier. The molecule may be either irreversiblyswitched from one state to the other (singly configurable) or reversiblyswitched from one state to the other (reconfigurable). The term“multi-stable” refers to a molecule with more than two such low energystates, or local minima.

[0055] The term “bimodal” for colorant molecules in accordance with thepresent invention may be designed to include the case of no, or low,activation barrier for fast but volatile switching. In this lattersituation, bistability is not required, and the molecule is switchedinto one state by the electric field and relaxes back into its originalstate upon removal of the field; such molecules are referred to as“bimodal”. In effect, these forms of the bimodal colorant molecules are“self-erasing”. In contrast, in bistable colorant molecules the colorantmolecule remains latched in its state upon removal of the field(non-volatile switch), and the presence of the activation barrier inthat case requires application of an opposite field to switch themolecule back to its previous state. Also, “molecular colorant” as usedhereinafter as one term to describe aspects of the present invention isto be distinguished from other chemical formulations, such as dyes,which act on a molecular level; in other words, “molecular colorant”used hereinafter signifies that the colorant molecules as described inthe Appendix and their equivalents are employed in accordance with thepresent invention.

[0056] Micron-scale dimensions refers to dimensions that range from 1micrometer to a few micrometers in size.

[0057] Sub-micron scale dimensions refers to dimensions that range from1 micrometer down to 0.05 micrometers.

[0058] Nanometer scale dimensions refers to dimensions that range from0.1 nanometers to 50 nanometers (0.05 micrometers).

[0059] Micron-scale and submicron-scale wires refers to rod orribbon-shaped conductors or semiconductors with widths or diametershaving the dimensions of 0.05 to 10 micrometers, heights that can rangefrom a few tens of nanometers to a micrometer, and lengths of severalmicrometers and longer.

[0060] “HOMO” is the common chemical acronym for “highest occupiedmolecular orbital”, while “LUMO” is the common chemical acronym for“lowest unoccupied molecular orbital”. HOMOs and LUMOs are responsiblefor electronic conduction in molecules and the energy difference betweenthe HOMO and LUMO and other energetically nearby molecular orbitals isresponsible for the color of the molecule.

[0061] An “optical switch,” in the context of the present invention,involves changes in the electro-magnetic properties of the molecules,both within and outside that detectable by the human eye, e.g., rangingfrom the far infra-red (IR) to deep ultraviolet (UV). Optical switchingincludes changes in properties such as absorption, reflection,refraction, diffraction, and diffuse scattering of electromagneticradiation.

[0062] The term “transparency” is defined within the visible spectrum tomean that optically, light passing through the colorant is not impededor altered except in the region in which the colorant spectrallyabsorbs. For example, if the molecular colorant does not absorb in thevisible spectrum, then the colorant will appear to have water cleartransparency.

[0063] The term “omni-ambient illumination viewability” is definedherein as the viewability under any ambient illumination condition towhich the eye is responsive.

[0064] As a general proposition, “media” in the context of the presentinvention includes any surface, whether portable or fixed, that containsor is layered with a molecular colorant or a coating containingmolecular colorant in accordance with the present invention wherein“bistable” molecules are employed; for example, both a flexible sheetexhibiting all the characteristics of a piece of paper and a writablesurface of an appliance (be it a refrigerator door or a computingappliance using the molecular colorant). “Display” (or “screen”) in thecontext of the present invention includes any apparatus that employs“bimodal” molecules, but not necessarily bistable molecules. Because ofthe blurred line regarding where media type devices ends and displaymechanisms begin, no limitation on the scope of the invention isintended nor should be implied from a designation of any particularembodiment as a “media” or as a “display.”

[0065] As will become apparent from reading the Detailed Description andAppendix, “molecule” can be interpreted in accordance with the presentinvention to mean a solitary molecular device, e.g., an optical switch,or, depending on the context, may be a vast array of molecular-leveldevices, e.g., an array of individually addressable, pixel-sized,optical switches, which are in fact linked covalently as a singlemolecule in a self-assembling implementation. Thus, it can be recognizedthat some molecular systems comprise a super-molecule where selectivedomain changes of individual molecular devices forming the system areavailable. The term “molecular system” as used herein refers to bothsolitary molecular devices used systematically, such as in a regulararray pixel pattern, and molecularly linked individual devices. Nolimitation on the scope of the invention is intended by interchangeablyusing these terms nor should any be implied.

[0066] General

[0067] As illustrated schematically in a magnified partial view in FIG.2AA, electronic print media 200 in accordance with one embodiment of thepresent invention comprises an electrochromic coating 201 affixedsuperjacently to a backing 202 substrate. The media 200 of the presentinvention employs an electrochromic molecular colorant coating 201 layer(phantom line illustration is used to demonstrate that the layer can infact be transparent as described hereinafter and also to denote that thelayer is very thin, e.g., on the order of a few microns) that containsbistable, electrochromic molecules 203 (represented by greatly magnifieddots) that undergo conformational changes as a result of application ofan electric field that in effect changes selectively localized regionsof this coating from one hue to another. In order to describe theinvention, the electrochromic molecules themselves are depicted assimple dots 203 in FIG. 2BB; however, it should be recognized that thereare literally millions of such molecules (in unlinked system terms) percubic micron of colorant; this can be thought of also as millions ofmolecular optical switching devices per cubic micron of colorant in alinked molecular system.

[0068] Optionally, note that as the molecular colorant is spatiallyaddressable at its molecular scale, the colorant molecules may becommingled with molecules of the substrate. Incorporated substratecoloration and fabrication processes are well known in the print mediaart.

[0069] Bichromal Molecules for Electrochromic Colorants

[0070] In order to develop a molecular colorant suitable for rewritablemedia, what is needed is a molecular system that avoids chemicaloxidation and/or reduction, permits reasonably rapid switching from afirst state to a second, is reversible to permit real-time or video ratewriting-erasing applications, and can be adapted for use in a variety ofoptical devices.

[0071] The present invention introduces the capability of usingmolecules for optical switches, in which the molecules change color whenchanging state. This property can be used for a wide variety ofwrite-read-erase devices or any other application enabled by a materialthat can change color or transform from transparent to colored. Thepresent invention introduces several new types of molecular opticalproperty switching mechanisms: (1) an electric (E) field inducedrotation of at least one rotatable section (rotor) of a molecule tochange the band gap of the molecule; (2) E-field induced chargeseparation or re-combination of the molecule via chemical bonding changeto change the band gap; (3) E-field induced band gap change via moleculefolding or stretching. These devices are generically considered to beelectric field devices, and are to be distinguished from electrochemicaldevices.

[0072] The co-pending U.S. Pat. Appl., partially incorporated herein asthe Appendix, by Zhang et al. for MOLECULAR MECHANICAL DEVICES WITH ABAND GAP CHANGE ACTIVATED BY AN ELECTRIC FIELD FOR OPTICAL SWITCHINGAPPLICATIONS, supra, describes in detail a plurality of embodiments ofbichromal molecules which can be used in accordance with the presentinvention.

[0073] With respect to the technology as described in the Appendix, theoverwhelming advantage of electrochromic molecular colorants overmicrocapsule technology (see, Background of the Invention, supra) forelectronic print media is realization of standardized, conventional hardcopy quality, print contrast, image resolution, switching speed, andcolor transparency. Such use of electrochromic molecular colorants willprovide readable content that resembles conventional printing dyes onpaper forms in color mode, color density, and coating layerincorporability. As depicted in FIG. 7AA, illustrating a stark contrastto the combined absorption-reflection physics of hemisphericmicrocapsule technology as depicted in FIG. 1DD, in the high colordensity state 701 (e.g., black), the electrochromic molecular colorant201 absorbs light uniformly at all light incidence angles and locationsto provide conventional ink color density. In the transparent state 703(FIG. 7AA, right side), the bichromal molecules 203 of the presentinvention do not absorb any visible light appreciably, allowing a mediasubstrate 202 to fully show through the coating layer 201. Thus, to theobserver an electrochromic molecular colorant image appearssubstantially identical to the image as it would appear in conventionalink print on paper. Namely, gradations of the specific high densitycolor, if any, are invisible to the naked eye. The term “electrochromicmolecular colorant” as used herein is expressly intended to include aplurality of different colorant molecules blended to form a layer thatcan achieve a desired composite color other than the exemplary blackstate.

[0074] Note additionally, the electrochromic molecular colorant isspatially addressable at its molecular (Angstrom) scale, allowing fargreater image resolution than the tens-of-microns-scale of microcapsulecolorants. As mentioned above, the molecules may be bistable or bimodal.When bistable, for example in an implementation that appears to be asimple sheet of print media, a variety of printing operation solutionsis available for pixel switching. While for a bistable molecularcolorant in accordance with the present invention a holding E-field viaan addressable matrix of electrodes is not necessary, nonetheless such amatrix may be used (such as for flash writing-erasing the entire sheet,then turning off the E-field to conserve power). For a bimodal, and thusself-erasing, implementation, an electrode array with a holding E-fieldis required. An exemplary, molecular wire adaptable for printing pixelsis described by Kuekes et al. in U.S. Pat. No. 6,128,214 for a MOLECULARWIRE CROSSBAR MEMORY (assigned to the common assignee herein andincorporated herein by reference).

[0075] Further, the color switching time for the electrochromicmolecular colorant pervaded pixel regions of the media 200 issignificantly shorter than that for microcapsule colorants, allowingsignificantly faster imaging speeds, in the main because theelectrochromic molecules of the colorant are substantially stationaryand change color either through the movement of electrons, the twistingof molecular elements, or both. In each case, the total mass in movementfor any addressed pixel is many orders of magnitude smaller than thatrequired with microcapsule colorants; note also that there isadditionally no viscous drag component .

[0076] Still further, electronic media 200 containing the electrochromicmolecular colorant coating layer(s) as described in detail hereinafterhave the durability of print on conventional media and are not subjectto colorant breakage through externally applied pressure in manufactureor use as is media coated with microcapsule colorants.

[0077] Thus, it is an advantageous feature of the present invention tohave a colorant material layer, comprising the bichromal molecules in aform to use as a coating, or film, for adaptable rewritable surfaces. Itis another advantageous feature of the present invention to provide aliquid form of the molecular colorant used to fabricate rewritablemedia, including fixed surfaces.

[0078] Electric Field Addressable Rewritable Media Using BichromalColorant

[0079] Turning now to FIGS. 2AA, 2BB, in a first embodiment the presentinvention comprises an electrical field addressable, rewritable media200 using a bichromal electrochromic molecular colorant. As the colorantis active at a molecular level, it may be formed in a number of ways.Embodiments that are self-assembling, formed using impregnation, or acoating with a liquid, paint, ink, or as an otherwise adapted formliquid vehicle on a substrate 202, are all within the scope of theinvention. The molecular colorant may be a self-assembling system orhave a carrier or vehicle for applying the colorant to a substrate usingconventional deposition and drying (or curing) techniques. The varioustypes of vehicles are discussed in more detail hereinbelow.

[0080] The present media 200 invention contemplates a wide variety ofsubstrate 202 materials and forms. As merely one example directed towardprinter and plain paper-like application uses, the coating 201 may beaffixed onto a plastic or other flexible, durable, material substrate202 in the approximate size, thickness, and shape of commercialstationery or other printable media (see also, U.S. Pat. No. 5,866,284by Kent D. Vincent, filed on May 28, 1997, for a PRINT METHOD ANDAPPARATUS FOR RE-WRITABLE MEDIUM; see also U.S. Patent Application Ser.No. ______, (HP docket no. 10010539) also by Vincent et al.). Theparticular substrate 202 composition implemented is fully dependent onthe specific application and, particularly, to the role that thesubstrate plays in supporting or creating the electric field that isimposed across the coating 201 layer. In fact, the molecular coating, atleast in a bistable molecular system form, can be used with any surfaceupon which writing or images can be formed.

[0081] The Molecular System Erasably Writable Surface

[0082] In a preferred embodiment related to the present invention, acoating layer 201 of the media 200 comprises electrochromic molecules203 (FIGS. 2AA-2BB)—self-assembling or molecules in association withanother chemical component, the “vehicle”—having an electrical fieldresponsive high color density state (hereinafter simply “color state”)and a transparent state, or two highly contrasting color states, e.g., ablack state and a color state (e.g., yellow). The vehicle may includebinders, solvents, flow additives, or other common coating additivesappropriate for a given implementation.

[0083] Preferably, the colorant of the coating 201 obtains a color state(e.g., black) when subjected to a first electrical field and atransparent state when subjected to a second electrical field. Thecoating 201—or more specifically, the addressable pixel regions of themedia 200—in a preferred embodiment is bistable; in other words, onceset or written, the field targeted, “colored pixel,” molecules form the“printed content,” remaining in the current printed state until thesecond field is applied, intentionally erasing the image by returningthe molecules to their transparent state at the field targeted pixels.Again, it must be recognized that there may be millions of such switchedmolecule in any given pixel. No holding electrical field is required tomaintain the printed content.

[0084] Alternately, the colorant may be monostable, obtaining alocalized, first color state (e.g., transparent) when subjected to alocalized electrical field, then configuratively relaxing to a secondcolor state (e.g., black) in the absence of the field, i.e., bichromaland self-erasing.

[0085] Although very different in constitution, the coating compositionof this invention is analogous to conventional coating formulationtechnology. The constituents of the colorant will depend on the rheologyand adhesion needs of the printing/coating process and substratematerial. In some implementations, the colorant strata will beself-assembling. Typically, the coating 201 layer will compose 1%-30% ofthe solid content of the film deposited to form the coating 201 layer onthe substrate 202. This amount is usually determined by desired imagecolor density. The coating 201 may include a polymeric binder to producea dried or cured coating 201 layer on the substrate 202 in which theelectrochromic molecular colorant is suspended. Alternatively, thesolids content may include as much as 100% colorant for certain knownmanner evaporative deposition methods or other thin film depositionmethods wherein the colorant, or an associated vehicle, is deposited. Inthe case of deposition-evaporation methods, there may be no associatedvehicle. In some instances, the colorant must be pre-oriented within thedeposited coating 201 layer to allow an optimum alignment with theelectrical field that will be used to write and erase a printed content.Such orientation may be achieved by solidifying the deposited coating201 layer under the influence of a simultaneously applied electric fieldacross the media 200. In one specific embodiment, the coating 201comprises electrochromic molecular colorant and a liquid, ultravioletlight (“UV”) curable, prepolymer (e.g., (meth)acrylate or vinylmonomers/oligomers). The polymer in this instance is formed in situ onthe media substrate 202 when subjected to ultraviolet radiation. Suchprepolymers are well known in the coatings art.

[0086] In a second specific embodiment, coating solidification may occurthrough thermally activated vehicle chemical reaction common to epoxy,urethane, and thermal free radical activated polymerization.

[0087] In a third specific embodiment, coating solidification may occurthrough partial or total vehicle evaporation.

[0088] The colorant may also self-orient through colorant/coating designthat allows a self-assembled lattice structure, wherein each colorantmonomer aligns with adjacent colorant monomers. Such design and latticestructures, for example, are common to dendrimers and crystals.Processes for self-assembly may include sequential monolayer depositionmethods, such as well known Langumir film and gas phase depositiontechniques.

[0089] The Substrate

[0090] The construction of any specific implementation of the media isdependent upon the writing means, such as are schematically representedin FIGS. 3AA, 4AA, and 5AA,described in more detail hereinafter. Inco-pending applications, the assignee has provided Detailed Descriptionof writing instruments and apparatus for writing using the molecularcolorant. For implementations using an electric field that isperpendicular to the surface of the media (see e.g., FIGS. 4AA and 5AA,the substrate 202 should be fabricated of a material having a dielectricconstant and electrical conductivity which compliments that of thecolorant coating 201 layer. Overall, the substrate may be flexible,semi-flexible, or rigid. It may comprise structures as a film, foil,sheet, fabric, or a more substantial, preformed, three-dimensionalobject. It may be electrically conductive, semi-conductive, orinsulative as appropriate for the particular implementation. Likewise,the substrate may be optically transparent, translucent or opaque, orcolored or uncolored, as appropriate for the particular implementation.Suitable substrate materials for one-side electrode implementations suchas demonstrated by FIG. 3AA may be composed, for example, of paper,plastic, metal, glass, rubber, ceramic, wood, synthetic and organicfibers, and combinations thereof. Suitable flexible sheet materials arepreferably durable for repeated imaging, including for example resinimpregnated papers (e.g. Appleton Papers Master Flex™), synthetic fibersheets (e.g., DuPont™ Tyvex™), plastic films (e.g., DuPont Mylar™,General Electric™ Lexant™, and the like) elastomeric films (e.g.,neoprene rubber, polyurethane, and the like), woven fabrics (e.g.,cotton, rayon, acrylic, glass, metal, ceramic fibers, and the like), andmetal foils. Suitable substrate materials for two-sided electrodeapplications as shown in FIGS. 4AA and 5AA may be composed from the samematerials wherein it is preferable that the substrate be conductive orsemi-conductive, have a conductive layer in near contact with themolecular colorant layer201, or have a high dielectric constant bulkproperty to minimize voltage drop across the substrate. Conductivesubstrates include metals, highly conjugated conductive polymers, ionicpolymers, salt and carbon filled plastics and elastomers, and the like.Suitable semi-conductive substrates may be composed of conventionaldoped silicon and the like. Substrates with a conductive layer includemetal clad printed circuit board, indium tin oxide coated glass,ceramics, and the like. Vapor deposited or grown semiconductor films onglass, ceramic, metal or other substrate material may also be used. Eachof these substrates are commercially available. High dielectric constantmaterials include metal-oxide ceramics such as titania. Suitablesubstrates may be composed of sintered ceramic forms, woven ceramicfabric, or ceramic filled plastics, elastomers and papers (viaceramic-resin impregnation). Translucent substrates may be used inapplications where ambient illumination and backlit viewing options aremade available on the same substrate. In general, it is desirable thatthe translucent substrate appear relatively opaque white under ambientviewing conditions and transparent white under backlit viewingconditions. Suitable translucent substrates include crystalline andsemi-crystalline plastic, fiber sheets and film (e.g., Dupont Tyvex),matte-surfaced plastic films (e.g., DuPont matte-finish Mylar andGeneral Electric matte-finish Lexan), commercial matte-surfaced glass,and the like.

[0091] Apparatus and Methodology

[0092] Turning now to FIG. 3AA, for an implementation such as a simplesheet of rewritable media or a mass data storage media (see Background,supra), or on other bistable molecular colorant coated surfaces where aholding field is not used, it is desirable to create an electricalwriting field from a single coating side, for example with an electronicpen tip or electrode pair 301 and 303, or 301, 305, and to entrain thefield across the coating 201 layer. In such instances, an appropriatelylow conductivity and dielectric constant colorant coating 201 isdesirable to prevent field shunting within the coating layer. Theelectrical properties of the substrate 202 are less important with suchfringe field (represented by dashed—arrow 307) type writing instruments.

[0093] For applications in which it is desirable to create the writingfield (dashed—arrow 401) perpendicularly through the media 200thickness, such as depicted in FIG. 4AA, with electrodes 403, 405 onopposing sides of the media, the substrate 202 preferably has a highdielectric constant, or high electrical conductivity if the adjacentelectrode is common to all pixels. These properties minimize the voltagedrop (loss) across the substrate 202 to minimize media switching voltagerequirement. For example, employable substrates 202 are represented bythe group: titania-filled plastic, certain high dielectric constantresin impregnated papers, and metals.

[0094] For certain implementations, e.g., large easel boards (note thatmolecular colorant based electronic displays and display screens, suchas those used in computers, PDA's and the like are described in otherco-pending applications by Vincent et al. and assigned to the commonassignee herein), it is desirable to coat substrates having an electrodeor array of electrodes included on the substrate surface to be coated.Representative substrates include metal-clad fiberboards, printedcircuit boards, metalized glass, surface etched metalized glass,graphite impregnated rubbers and plastics, sheet metals, and the like.

[0095] Turning now to FIG. 5AA, in a more costly embodiment, the media200′ may include a substrate 202 having a reflective substrate 501coated with a preferred background color layer 503, wherein thebackground color remains fixed and independent of the imposed electricwriting fields (dashed—arrow 505). This surface 501 will normally createthe background color of the media 200′ when the molecular colorantcoating 201 layer is switched to the transparent state. Such surfacecoatings generally comprise a conventional pigment or colorantincorporated in a polymer binder. As with the substrate 202, the surface501 coating 503 comprises a binder and colorant of a composition chosento maintain the integrity of the electric field 505 imposed on the media200′ and to minimize additional voltage drop across the media.Alternatively, a conventional pigment or colorant may be incorporated inthe substrate 202 itself. Such surface coating and incorporatedsubstrate coloration fabrication processes are well known in the mediaart.

[0096] The media 200′ of the present invention may further include aprotective surface 507 layer. In general, the protective surface layer507 is visibly transparent and protects the colorant coating 201 fromabrasion, photo-oxidative color fade, chemical decomposition, or otherenvironmentally imposed factors that may alter the integrity of themedia 200′. The protective surface layer 507 fabrication can be in aknown manner, such as a polymeric coating, a transparent materialdeposition, or a laminate. As examples, polymethyl methacrylate andpolyurethane type polymeric coatings are known to contain ultravioletradiation absorbing additives; thin film, vapor deposited, glass; andpolymer laminate films may be employed. Methods of layer application arealso well known in the art. As with the substrate 202, the protectivesurface layer 507 is preferably composed to maintain the integrity ofthe electric field imposed on the media and to minimize additionalvoltage drop across the media.

[0097] The colorant coating 201 of any of the aforementioned media 200,200′ of this invention may comprise a mosaic pattern of alternatingcolorant molecule pixel regions that are common to the same coatingplane. Such alternating colors may include, for example, a repeatingpattern of cyan, magenta and yellow pixels. Mosaic patterns for colordisplays are well known in the display art and are useful to the presentinvention for producing color images. Achievable resolution is fineenough so that contiguous print content regions of a color can beattained in a manner that is substantially seamless to the naked eye. Anumber of printing processes are well suited for accurate deposition ofeach colored pixel in the mosaic. Such processes include: offsetlithography, gravure, silkscreen, ink-jet, electrophotography, andphotomask deposition. Ink-jet offers a particularly attractive mosaicdeposition means from the viewpoint of small controlled dot shapes andplacement in a non-contact deposition process. For most applications,the pattern of pixels in the mosaic must coincide with the pattern ofelectrodes constructed to drive each pixel. Furthermore, a mosaicpattern may also be formed by printing mosaic color pattern asbackground or by the use of conventional mosaic filters as part of, oradjacent to, a protective layer. The present embodiment shows use ofblack and transparent state molecules (see, e.g., FIG. 7) which can beused as a layer over a pre-printed color mosaic background (e.g.,printed conventionally such as with a CYM ink-jet apparatus). No colorshows through in the black switch state and color shows through in thetransparent switch state. Likewise the use of a conventional colorfilter (e.g., as used in color LCD screens) for backlit or projectiondisplay use can be implemented; the back-transparent colorant moleculesserves as a light valve similar to liquid crystal shutters. The benefitof each of these approaches is that it uses a single molecular colorantwith conventional mosaic colorant (ink, filters). The color mosaicfilter may optionally be printed as a background layer on an otherwisetransparent substrate (e.g., glass). These approaches allow full colorwithout inherent color, switched molecules (e.g., yellow/transparentstate, and the like).

[0098] Importantly, because the colorant molecules can be implemented inan embodiment having a transparent state, colorant strata can be layered(e.g., molecules switching between transparent and primary colors inseparate strata layers) such that very high resolution, full colorrendering can be accomplished through multi-color layer pixelsuperposition (e.g., overlays of the subtractive primary colors cyan,magenta and, yellow); only in the present invention such implementationswill be in fully rewritable formats. As noted in the Background section,this solves one of the limitations inherent in the microcapsuletechnologies.

[0099] The thickness and dielectric constant of each coating, layer andsubstrate component comprising the media 200, 200′ of this invention ispreferably selected to accommodate the spacing of opposing electrodes,field geometry, and voltage used to switch a given media pixel. Thepixel resolution, as measured in pixels per linear dimension (e.g., 1200pixels/inch (“ppi”) for color, 4800 ppi for grey scale), is inverselyproportional to the electrode spacing. The pixel switching voltage forthe embodiment as shown in FIG. 5AA is equivalent to the sum of voltagedrops over the respective layers that interpose the opposing electrodes.This is represented by the electrical schematic of FIG. 6AA. Each layerintroduces a series capacitance with a voltage drop, “V_(n),”proportional to the layer thickness (“d_(n)”) and inversely proportionalto the layer dielectric constant (“k_(n)”), where

[0100] “q”=the electronic charge (Coulombs) accumulated at an electrode,

[0101] “ε”=the permitivity constant, and

[0102] “A”=coating layer surface area subjected to the field.

[0103] The substrate 202 generally represents a significant voltage dropand source for electrical field broadening if included within theelectrode field. Thus, the substrate 202 is preferably a conductivematerial, thereby making an effective common ground plane electrode inapplications such as FIGS. 4AA and 5AA that require the substrate to liewithin the writing electric field. Metals and conductive and ionicpolymers are good material choices in such instances. Alternatively, thesubstrate 202 may be composed of a high dielectric material to offsetthe voltage loss in an embodiment represented schematically by FIG. 4AA.Titania, or a like high dielectric filler, impregnated polymers,fiber-based papers, and plastics may be used for this purpose.

[0104] Exemplary Usefulness

[0105] Erasably Writeable Media

[0106] The electrochromic molecular colorant system in accordance withthe present invention may be described in part as an electrochromicmolecular colorant allowing incorporation into virtually all types ofinks, paints, coatings, and the like, where conventional colorants arecommonly used. Further, it may be applied to a substrate using most anyof the standard processes in which conventional pigments are used. Thesebenefits are, again, in stark contrast to microcapsule colorants wherethe size and fragile nature of the microcapsules prevents both stableliquid dispersion and subjection to physical forces common to moststandard application processes.

[0107] Solutions containing the electrochromic molecular colorant of thepresent invention may be, for example, spray, dip, roller, cast or knifecoated onto large surfaces or webs of material, such as paper or plasticfilms to form the rewritable region of the surfaces or webs. Moreover,the adaptability of the molecular colorant of the present invention tostandard application processing allows virtually any surface forexample, refrigerator doors, white boards, desktops, wristwatchsurfaces, computer display fascia, or any surface on which note takingmay be desirable—to be coated with the electric field rewritableelectrochromic molecular colorant having the molecular colorant therein.

[0108] Using bistable, bichromal molecular colorant, such surfaces thenmay be written and erased with devices capable of producing aselectively localized electric field within the coating. Paper-likesheets, surface coated with the electrochromic molecular colorant of thepresent invention, may be imaged with printers capable of producingpixel-sized electric fields, for example, through an electrode array.These writing-erasing apparatus, devices, and methods of operation arethe subject of other patent applications by Kent Vincent et al.,Hewlett-Packard, assignee.

[0109] Inks or paints containing the present electrochromic molecularcolorant may be selectively printed on various substrates, for example,to produce rewritable areas on a pre-printed form where the pre-printedareas are printed using non-erasable, conventional ink. Such rewritableareas may be printed with the molecular colorant using conventionaloffset lithography, gravure, intaglio, silkscreen, ink-jet processes, orthe like.

[0110] Note that some such erasably writable areas may includebacklighting, wherein the electrochromic molecular colorant ink isprinted on a transparent substrate for overhead projection use, or maybe printed on a white substrate for passive light viewing. In thebacklit configuration, a mosaic of electrochromic molecular colorantpixels may be used as an active color filter for projection displays. Inthe passive light configuration, the mosaic of electrochromic molecularcolorant pixels may form a stationary print-on-paper-like stationary.The electrochromic molecular colorant requires no passage of current andis, therefore, less subjected to display life reducing processes such asoxidation and charge trapping. Such passive light displays also offerbetter viewing under natural lighting conditions. Generally, theelectrochromic molecular colorant requires far less drive energy thanknown electronic display means since it does not emit light or requirebacklighting. Further energy savings is realized through optionalbi-stable colorant color states. Unlike liquid crystals, the bi-stableelectrochromic molecular colorant does not require a field to hold agiven image.

[0111] Data Storage Applications

[0112] The present invention electrochromic molecular colorant offerssignificant storage density, cost and write speed benefits overconventional ferromagnetic coating and CD-ROM storage media. The datastorage element in this instance becomes a bi-stable, twoelectro-optical states molecule, or more accurately an approximatemolecule-wide, or larger, column of layered molecules, that is writtenthrough a selectively localized electric field and read optically or byelectric field sensing. Optical reading electrical field sensingapplications are well known in the art. The molecular storage elementprovides significant storage density advantage over the much largermagnetic crystal or laser readable pit storage elements. Theelectrochromic molecular colorant may be incorporated in a polymer resinand inexpensively coated on standard storage media substrates using mostany standard continuous thick film coating method. Thin film depositioncoating methods may also be used. Depending on colorant structure andbi-stability, the bit writing time is expected to range between 10⁻³ and10⁻⁹ seconds (based on computer simulations).

[0113] Summary

[0114] The present invention provides an electrochromic molecularcolorant 201 and a plurality of uses as an erasably writeable medium201. Multitudinous types of substrates, such as paper, 202 are adaptablefor receiving a coating of the colorant. Electrical fringe field 307 orthrough fields 401, 501 are used to transform targeted pixel moleculesbetween a first, high color state 701 and a second, contrasting state ortransparent state 703, providing information content having resolutionand viewability at least equal to hard copy document print.

[0115] The foregoing description of the preferred embodiment of thepresent invention has been presented for purposes of illustration anddescription. It is not intended to be exhaustive or to limit theinvention to the precise form or to exemplary embodiments disclosed.Obviously, many modifications and variations will be apparent topractitioners skilled in this art. Similarly, any process stepsdescribed might be interchangeable with other steps in order to achievethe same result. The embodiment was chosen and described in order tobest explain the principles of the invention and its best mode practicalapplication, thereby to enable others skilled in the art to understandthe invention for various embodiments and with various modifications asare suited to the particular use or implementation contemplated. It isintended that the scope of the invention be defined by the claimsappended hereto and their equivalents. Reference to an element in thesingular is not intended to mean “one and only one” unless explicitly sostated, but rather means “one or more.” Moreover, no element, component,nor method step in the present disclosure is intended to be dedicated tothe public regardless of whether the element, component, or method stepis explicitly recited in the following claims. No claim element hereinis to be construed under the provisions of 35 U.S.C. Sec. 112, sixthparagraph, unless the element is expressly recited using the phrase“means for . . . ” and no process step herein is to be construed underthose provisions unless the step or steps are expressly recited usingthe phrase “comprising the step(s) of . . . ”

What is claimed is:
 1. A colorant for a substrate, the colorantcomprising: a molecular system, said system including electrochromic,switchable molecules, each of said molecules being selectivelyswitchable between at least two optically distinguishable states,wherein said system is distributable on the substrate thereby forming anerasably writable surface.
 2. The colorant as set forth in claim 1comprising: said molecules exhibit an electric field induced band gapchange.
 3. The colorant as set forth in claim 2 comprising: saidelectric field induced band gap change occurs via a mechanism selectedfrom a group including (1) molecular conformation change or anisomerization, (2) change of extended conjugation via chemical bondingchange to change the band gap, and (3) molecular folding or stretching.4. The colorant as set forth in claim 2 comprising: said electric fieldinduced band gap change occurs via a molecular conformation change or anisomerization.
 5. The colorant as set forth in claim 4 wherein themolecules forming the molecular system further comprise: at least onestator portion and at least one rotor portion, wherein said rotorrotates from a first state to a second state with an applied electricfield, wherein in said first state, there is extended conjugationthroughout said molecular system, resulting in a relatively smaller bandgap, and wherein in said second state, said extended conjugation isdestroyed, resulting in a relatively larger band gap.
 6. The colorant asset forth in claim 4 comprising: dependent upon direction of electricalfield applied, in a first of said states said molecules are in a moreconjugated state having a relatively smaller band gap, and in a secondof said states said colorant molecules are in a less conjugated state,having a relatively larger band gap.
 7. The colorant as set forth inclaim 2 comprising: said electric field induced band gap change occursvia a change of extended conjugation via chemical bonding change tochange the band gap.
 8. The colorant as set forth in claim 7 comprising:said electric field induced band gap change occurs via a change ofextended conjugation via charge separation or recombination accompaniedby increasing or decreasing band localization.
 9. The colorant as setforth in claim 8 comprising: a change from a first state to a secondstate occurs with an applied electric field, said change involvingcharge separation in changing from said first state to said secondstate, resulting in a relatively larger band gap state, with lessπ-delocalization, and recombination of charge in changing from saidsecond state to said first state, resulting in a relatively smaller bandgap state, with greater π-delocalization.
 10. The colorant as set forthin claim 7 comprising: said electric field induced band gap changeoccurs via a change of extended conjugation via charge separation orrecombination and π-bond breaking or formation.
 11. The colorant as setforth in claim 10 comprising: a change from a first state to a secondstate occurs with an applied electric field, said change involvingcharge separation in changing from said first state to said secondstate, wherein in said first state there is extended conjugationthroughout, resulting in a relatively larger band gap state, and whereinin said second state said extended conjugation is destroyed andseparated positive and negative charges are created, resulting in arelatively smaller band gap state.
 12. The colorant as set forth inclaim 2 comprising: said electric field induced band gap change occursvia a molecular folding or stretching.
 13. The colorant as set forth inclaim 12 comprising: said colorant has three portions, a first portionand a third portion, each bonded to a second, central portion, wherein achange from a first state to a second state occurs with an appliedelectric field, said change involving a folding or stretching about ofsaid second portion, wherein in said first state there is extendedconjugation, resulting in a relatively smaller band gap state, andwherein in said second state, said extended conjugation is destroyed,resulting in a relatively larger band gap.
 14. The colorant as set forthin claim 1 comprising: said molecules are bistable, providing anon-volatile component.
 15. The colorant as set forth in claim 1comprising: a plurality of layers of molecular colorant strata whereinin each said strata molecules between a transparent state and a primarycolor state full color imaging is renderable through multi-color layerpixel superposition.
 16. The colorant as set forth in claim 1comprising: said molecules have a low activation barrier betweendifferent said states providing a fast volatile switch.
 17. The colorantas set forth in claim 1 comprising: said molecules have more than twosaid states, switchable such that optical properties can be tuned eithercontinuously by application of a decreasing or increasing electric fieldto form a volatile switch or color of selected composition regions ischanged abruptly by application of voltage pulses to switch with atleast one molecular activation barrier.
 18. The colorant as set forth inclaim 1 comprising: said system changes selected molecules between atransparent state and a colored state.
 19. The colorant as set forth inclaim 1 comprising: said system is configured for switching selectedpicture elements formed by said molecules between two visuallydistinctive color states.
 20. The colorant as set forth in claim 1comprising: said molecular system is configured for switching selectedpicture elements formed by said molecules between a transparent stateand a color state.
 21. The colorant as set forth in claim 1 comprising:said molecular system changes between one index of refraction andanother index of refraction.
 22. The colorant as set forth in claim 1comprising: said molecules are bistable.
 23. The colorant as set forthin claim 1 comprising: said molecules are bimodal.
 24. The colorant asset forth in claim 1 wherein said molecules are arranged to formdiscrete, addressable picture elements of a surface of said substrate.25. The colorant as set forth in claim 24 wherein said picture elementsconsist of a mosaic pattern of said molecules wherein said pattern hasoptically combinable visual color states.
 26. The colorant as set forthin claim 24 wherein said picture elements consist of a mosaic pattern ofsaid molecules wherein said pattern forms a mosaic of primary colors.27. The colorant as set forth in claim 24 wherein said molecules areselectively switchable between a transparent state and an opaque stateand are distributed across said substrate as an overlay of a mosaicpattern of primary color subpixel regions.
 28. The colorant as set forthin claim 24 where the colorant is printed on a white substrate forpassive light viewing.
 29. The colorant as set forth in claim 24 whereinthe colorant is printed on a transparent substrate for overheadprojection use.
 30. A writeable-erasable coating for a substrate,comprising: a carrier; and within said carrier, a composition includingelectrochromic switchable molecules, each of said molecules beingselectively switchable between at least two optically distinguishablestates, wherein said molecules are distributable on the substratethereby forming an erasably writable surface.
 31. An erasable writingmedium comprising: a substrate; and at least one layer of a molecularcolorant coating affixed to said substrate, wherein molecules of thecoating are at least bichromal and selectively switchable between colorstates under influence of a localized electric field.
 32. The medium asset forth in claim 31 comprising: said molecules are switchable betweena transparent state and a black state.
 33. The medium as set forth inclaim 31 comprising: said molecules are switchable between a transparentstate and a primary color state.
 34. The medium as set forth in claim 33comprising: said molecular colorant coating is a layer of mosaicallypatterned molecules having an electrically addressable subpixelarrangement such that full color combinations can render a pixel in aplurality of hues.
 35. The medium as set forth in claim 32 comprising:said colorant layer is an overlay for a mosaic pattern of primary colorpicture elements.
 36. The medium as set forth in claim 31 comprising:said molecules exhibit an electric field induced band gap change. 37.The medium as set forth in claim 36 comprising: said electric fieldinduced band gap change occurs via a mechanism selected from a groupincluding (1) molecular conformation change or an isomerization, (2)change of extended conjugation via chemical bonding change to change theband gap, and (3) molecular folding or stretching.
 38. The medium as setforth in claim 36 comprising: said electric field induced band gapchange occurs via a molecular conformation change or an isomerization.39. The medium as set forth in claim 38 wherein the molecules formingthe molecular system further comprise: at least one stator portion andat least one rotor portion, wherein said rotor rotates from a firststate to a second state with an applied electric field, wherein in saidfirst state, there is extended conjugation throughout said molecularsystem, resulting in a relatively smaller band gap, and wherein in saidsecond state, said extended conjugation is destroyed, resulting in arelatively larger band gap.
 40. The medium as set forth in claim 38comprising: dependent upon direction of electrical field applied, in afirst of said states said molecules are in a more conjugated statehaving a relatively smaller band gap, and in a second of said statessaid colorant molecules are in a less conjugated state, having arelatively larger band gap.
 41. The medium as set forth in claim 36comprising: said electric field induced band gap change occurs via achange of extended conjugation via chemical bonding change to change theband gap.
 42. The medium as set forth in claim 41 comprising: saidelectric field induced band gap change occurs via a change of extendedconjugation via charge separation or recombination accompanied byincreasing or decreasing band localization.
 43. The medium as set forthin claim 42 comprising: a change from a first state to a second stateoccurs with an applied electric field, said change involving chargeseparation in changing from said first state to said second state,resulting in a relatively larger band gap state, with lessπ-delocalization, and recombination of charge in changing from saidsecond state to said first state, resulting in a relatively smaller bandgap state, with greater π-delocalization.
 44. The medium as set forth inclaim 41 comprising: said electric field induced band gap change occursvia a change of extended conjugation via charge separation orrecombination and π-bond breaking or formation.
 45. The medium as setforth in claim 44 comprising: a change from a first state to a secondstate occurs with an applied electric field, said change involvingcharge separation in changing from said first state to said secondstate, wherein in said first state there is extended conjugationthroughout, resulting in a relatively larger band gap state, and whereinin said second state said extended conjugation is destroyed andseparated positive and negative charges are created, resulting in arelatively smaller band gap state.
 46. The medium as set forth in claim36 comprising: said electric field induced band gap change occurs via amolecular folding or stretching.
 47. The medium as set forth in claim 46comprising: said colorant has three portions, a first portion and athird portion, each bonded to a second, central portion, wherein achange from a first state to a second state occurs with an appliedelectric field, said change involving a folding or stretching about ofsaid second portion, wherein in said first state there is extendedconjugation, resulting in a relatively smaller band gap state, andwherein in said second state, said extended conjugation is destroyed,resulting in a relatively larger band gap.
 48. The medium as set forthin claim 31 comprising: said molecules are bistable, providing anon-volatile component.
 49. The medium as set forth in claim 31comprising: said molecules have a low activation barrier betweendifferent said states providing a fast volatile switch.
 50. The mediumas set forth in claim 31 comprising: said molecules have more than twosaid states, switchable such that optical properties can be tuned eithercontinuously by application of a decreasing or increasing electric fieldto form a volatile switch or color of selected composition regions ischanged abruptly by application of voltage pulses to switch with atleast one molecular activation barrier.
 51. The medium as set forth inclaim 31 comprising: said system is configured for switching selectedpicture elements formed by said molecules between two visuallydistinctive color states.
 52. The medium as set forth in claim 31comprising: said molecular system is configured for switching selectedpicture elements formed by said molecules between a transparent stateand a color state.
 53. The medium as set forth in claim 31 comprising:said molecular system changes between one index of refraction andanother index of refraction.
 54. The medium as set forth in claim 31comprising: said molecules are bistable.
 55. The medium as set forth inclaim 31 comprising: said molecules are bimodal.
 56. The medium as setforth in claim 31 wherein said molecules are arranged to form discrete,addressable subpixels of a surface of said substrate.
 57. The medium asset forth in claim 56 wherein said subpixels consist of a mosaic patternof said molecules wherein said pattern has optically combinable visualcolor states.
 58. The medium as set forth in claim 56 wherein saidsubpixels consist of a mosaic pattern of said molecules wherein saidpattern forms a mosaic of primary colors.
 59. The medium as set forth inclaim 56 wherein said molecules are selectively switchable between atransparent state and an opaque state and are distributed across saidsubstrate as an overlay of a mosaic pattern of primary color subpixelregions printed on said substrate.
 60. The medium as set forth in claim56 where the colorant is printed on a white substrate for passive lightviewing.
 61. The medium as set forth in claim 56 wherein the colorant isprinted on a transparent substrate for overhead projection use.
 62. Themedium as set forth in claim 31 comprising: said substrate is a materialthat is both flexible and durable for repeated imaging.
 63. The mediumas set forth in claim 62 wherein said flexible material is configured asa cut sheet print medium.
 64. The medium as set froth in claim 62wherein said flexible material is configured as a web print medium. 65.A method for writing on electrical field addressable rewritable medium,the method comprising: providing a substrate having at least one layerof a molecular colorant coating wherein molecules of the coating are atleast bichromal and subjectable to switching between color states underinfluence of a localized electric field and wherein said layer isdistributed across said substrate forming pixels on said medium; andelectrically addressing pixels by selectively controlling each saidlocalized electric field to form document content on said medium.
 66. Adata storage device comprising: a substrate; and at least one layer of amolecular colorant coating wherein molecules of the coating are at leastbichromal and subject to bistable switching between at least twoelectro-optical states under influence of a localized electric field.67. The data storage device as set forth in claim 66 comprising: saidmolecules exhibit an electric field induced band gap change.
 68. Thedata storage device as set forth in claim 65 comprising: said electricfield induced band gap change occurs via a mechanism selected from agroup including (1) molecular conformation change or an isomerization,(2) change of extended conjugation via chemical bonding change to changethe band gap, and (3) molecular folding or stretching.
 69. The datastorage device as set forth in claim 67 comprising: said electric fieldinduced band gap change occurs via a molecular conformation change or anisomerization.
 70. The data storage device as set forth in claim 69wherein the molecules forming the molecular system further comprise: atleast one stator portion and at least one rotor portion, wherein saidrotor rotates from a first state to a second state with an appliedelectric field, wherein in said first state, there is extendedconjugation throughout said molecular system, resulting in a relativelysmaller band gap, and wherein in said second state, said extendedconjugation is destroyed, resulting in a relatively larger band gap. 71.The data storage device as set forth in claim 69 comprising: dependentupon direction of electrical field applied, in a first of said statessaid molecules are in a more conjugated state, having a relativelysmaller band gap, and in a second of said states said colorant moleculesare in a less conjugated state, having a relatively larger band gap. 72.The data storage device as set forth in claim 67 comprising: saidelectric field induced band gap change occurs via a change of extendedconjugation via chemical bonding change to change the band gap.
 73. Thedata storage device as set forth in claim 72 comprising: said electricfield induced band gap change occurs via a change of extendedconjugation via charge separation or recombination accompanied byincreasing or decreasing band localization.
 74. The data storage deviceas set forth in claim 73 comprising: a change from a first state to asecond state occurs with an applied electric field, said changeinvolving charge separation in changing from said first state to saidsecond state, resulting in a relatively larger band gap state, with lessπ-delocalization, and recombination of charge in changing from saidsecond state to said first state, resulting in a relatively smaller bandgap state, with greater π-delocalization.
 75. The data storage device asset forth in claim 72 comprising: said electric field induced band gapchange occurs via a change of extended conjugation via charge separationor recombination and π-bond breaking or formation.
 76. The data storagedevice as set forth in claim 75 comprising: a change from a first stateto a second state occurs with an applied electric field, said changeinvolving charge separation in changing from said first state to saidsecond state, wherein in said first state there is extended conjugationthroughout, resulting in a relatively larger band gap state, and whereinin said second state said extended conjugation is destroyed andseparated positive and negative charges are created, resulting in arelatively smaller band gap state.
 77. The data storage device as setforth in claim 67 comprising: said electric field induced band gapchange occurs via a molecular folding or stretching.
 78. The datastorage device as set forth in claim 77 comprising: said colorant hasthree portions, a first portion and a third portion, each bonded to asecond, central portion, wherein a change from a first state to a secondstate occurs with an applied electric field, said change involving afolding or stretching about of said second portion, wherein in saidfirst state there is extended conjugation, resulting in a relativelysmaller band gap state, and wherein in said second state, said extendedconjugation is destroyed, resulting in a relatively larger band gap. 79.The data storage device as set forth in claim 66 comprising: saidmolecules are bistable, providing a non-volatile component.
 80. The datastorage device as set forth in claim 66 comprising: said molecules havea low activation barrier between different said states providing a fastvolatile switch.
 81. The data storage device as set forth in claim 66comprising: said molecules have more than two said states, switchablesuch that electro-optical properties can be tuned either continuously byapplication of a decreasing or increasing electric field to form avolatile switch or color of selected composition regions is changedabruptly by application of voltage pulses to switch with at least onemolecular activation barrier.
 82. The data storage device as set forthin claim 66 comprising: said system is configured for switching selectedmemory elements formed by said molecules between two distinctiveelectro-optical states.
 83. The data storage device as set forth inclaim 66 comprising: said molecular system is configured for switchingselected memory elements formed by said molecules between a transparentstate and a color state.
 84. The data storage device as set forth inclaim 66 comprising: said molecular system changes between one index ofrefraction and another index of refraction.
 85. A method of fabricatingrewritable media, the method comprising: providing a substrate; andforming with said substrate, a rewritable layer wherein thewritable-erasable layer is formed by a molecular system, said systemincluding electrochromic switchable molecules, each of said moleculesbeing selectively switchable between at least two opticallydistinguishable states.
 86. The method as set forth in claim 85 whereinsaid molecules exhibit an electric field induced band gap change. 87.The method as set forth in claim 86 wherein said electric field inducedband gap change occurs via a mechanism selected from a group including(1) molecular conformation change or an isomerization, (2) change ofextended conjugation via chemical bonding change to change the band gap,and (3) molecular folding or stretching.
 88. The method as set forth inclaim 86 wherein said electric field induced band gap change occurs viaa molecular conformation change or an isomerization.
 89. The method asset forth in claim 88 wherein the molecules forming the molecular systeminclude at least one stator portion and at least one rotor portion,wherein said rotor rotates from a first state to a second state with anapplied electric field, wherein in said first state, there is extendedconjugation throughout said molecular system, resulting in a relativelysmaller band gap, and wherein in said second state, said extendedconjugation is destroyed, resulting in a relatively larger band gap. 90.The method as set forth in claim 88 wherein, dependent upon direction ofelectrical field applied, in a first of said states said molecules arein a more conjugated state, having a relatively smaller band gap, and ina second of said states said colorant molecules are in a less conjugatedstate, having a relatively larger band gap.
 91. The method as set forthin claim 86 wherein said electric field induced band gap change occursvia a change of extended conjugation via chemical bonding change tochange the band gap.
 92. The method as set forth in claim 91 whereinsaid electric field induced band gap change occurs via a change ofextended conjugation via charge separation or recombination accompaniedby increasing or decreasing band localization.
 93. The method as setforth in claim 92 wherein a change from a first state to a second stateoccurs with an applied electric field, said change involving chargeseparation in changing from said first state to said second state,resulting in a relatively larger band gap state, with lessπ-delocalization, and recombination of charge in changing from saidsecond state to said first state, resulting in a relatively smaller bandgap state, with greater π-delocalization.
 94. The method as set forth inclaim 91 wherein said electric field induced band gap change occurs viaa change of extended conjugation via charge separation or recombinationand π-bond breaking or formation.
 95. The method as set forth in claim94 wherein a change from a first state to a second state occurs with anapplied electric field, said change involving charge separation inchanging from said first state to said second state, wherein in saidfirst state there is extended conjugation throughout, resulting in arelatively larger band gap state, and wherein in said second state saidextended conjugation is destroyed and separated positive and negativecharges are created, resulting in a relatively smaller band gap state.96. The method as set forth in claim 86 wherein said electric fieldinduced band gap change occurs via a molecular folding or stretching.97. The method as set forth in claim 96 wherein said colorant has threeportions, a first portion and a third portion, each bonded to a second,central portion, wherein a change from a first state to a second stateoccurs with an applied electric field, said change involving a foldingor stretching about of said second portion, wherein in said first statethere is extended conjugation, resulting in a relatively smaller bandgap state, and wherein in said second state, said extended conjugationis destroyed, resulting in a relatively larger band gap.
 98. The methodas set forth in claim 85 wherein said molecules are bistable, providinga non-volatile component.
 99. The method as set forth in claim 85wherein said molecules have a low activation barrier between differentsaid states providing a fast volatile switch.
 100. The method colorantas set forth in claim 85 wherein said molecules have more than two saidstates, switchable such that optical properties can be tuned eithercontinuously by application of a decreasing or increasing electric fieldto form a volatile switch or color of selected composition regions ischanged abruptly by application of voltage pulses to switch with atleast one molecular activation barrier.